Third Generation mobile communication technology (3G) generally refers to a new generation of a mobile communication system that integrates multimedia communications such as wireless communication and internet. Such mobile communication system is able to process various types of media such as image, music, video streams and provide various information services such as web page browsing, teleconference, e-commerce. However, with the development of the communication technology, people are setting more and more demanding requirements for the mobile communication. The network architecture and protocols of the existing 3rd Generation Partnership Project (3GPP) no longer satisfy users' high demand for mobile communication. Accordingly, 3GPP proposes a concept of an evolved network for fulfilling a future communication requirement.
To guarantee the competitive edge of the 3GPP in the further, especially the capability of 3GPP system for processing rapidly increasing IP data service, 3GPP has launched a Long Term Evolution (LTE) program and a System Architecture Evolution (SAE) program. The purpose of LTE is to provide an evolved network which can reduce time delay, increase user data rate, enhance system capability and coverage and save overall cost of the operators. Meanwhile, the evolved network structure is also an important indicator for the backward compatibility of the existing network.
The evolved network structure needs to meet the following requirements.
(1) basic IP connection needs to be set up in the evolved network during an initial stage when a user equipment accesses a network.
(2) the evolved network structure must minimize the delay of the user data
(3) each function module in the evolved network architecture should be defined in such a way to avoid function overlap or repetition so as to avoid unnecessary signaling and time delay.
FIG. 1 illustrates a popular network architecture derived from the above. The network architecture mainly includes four logic function modules: a Mobility Management Entity (MME), a user plane entity (SAE) gateway including two Serving Gateways (S-GW), a PDN Gateway (P-GW), an LTE Radio Access Network (LTE RAN), and a Home Subscriber Server (HSS), etc. MME is a mobility management module responsible for mobility management for a control plane, including management for user context and mobility status, assignment of information such as user temporary identity, mobility status, tracking area (TA), and verification of user identity. The MME corresponds to a control plane of a Serving GPRS Support Node (SGSN) in the Universal Mobile Telecommunications System (UMTS). S-GW is a Serving Gateway responsible for initiating paging downstream data of a user equipment (UE) in idle mode, managing and storing UE context, IP bearer parameter and routing information in the network, and managing UE's mobility control plane anchor and a user plane anchor functions between 3G and SAE network. The S-GW corresponds to a data plane of SGSN in the current UMTS. P-GW is responsible for a user anchor function that UE accesses the packet data network. The P-GW has packet routing and forwarding functions and is responsible for policy charging enhancement, packet filtering function based on each user, and is coupled to S-GW to carry and deliver control information such as create/modify/delete. LTE RAN is a radio access network for the evolved network. The nodes therein are not defined specifically. Generally, the LTE RAN includes an evolved base station (eNodeB), and may also include a control plane server (CPS) logic entity. In a logic sense, the LTE RAN can be treated as a Long Term Evolution Radio Access Network (LTE-RAN) entity.
Since network structures adopting different radio access technologies (RAT) may exist simultaneously in a real application, network registration procedures may be aroused in a ping-pang manner due to the change between different networks when UE is moving between different RATs (e.g., network and evolution network 2G/3G). As illustrated in FIG. 2, Routing Area 1 (RA1) and Routing Area 2 (RA2) are routing areas for an existing 2G/3G. The UE of the existing 2G/3G always initiates a Routing Area Update (RAU) procedure when switching a routing area (RA). Of course, even if UE does not switch RA, there is also a periodic location update procedure, the function of which is to inform the network that the UE is still in the network currently so as to prevent the network from keeping paging UE without knowing that the UE leaves the network. A network registration procedure due to the movement of the UE is now illustrated below.
In FIG. 2, TA1, TA2, TA3, TA4 are tracking areas in the evolved network. TA is similar to RA in 2G/3G. When a multi-mode UE is moving between different RA and TA, to guarantee that the UE can be paged in networks adopting different RATs, the UE needs to register with RA and TA it enters. If the UE enters RA1, the UE needs to register with SGSN of 2G/3G. When the UE enters TA1, the UE further needs to register with MME of the evolved network. When the UE exits TA1 and re-enters RA1, the UE needs to register with SGSN of 2G/3G again. However, the method results in frequent network registration procedures for guarantee the paging, causing thereby considerable consumption of registration signaling.
To solve the problem, various methods in conventional arts have been proposed to avoid frequent network registrations and a severe waste in the air-interfaces. Currently, a schema for lessening the registration/update influence on air-interfaces imposed by UE in idle mode when entering networks with different RATs. The idea of the schema is that the UE registers with an access network (2G/3G network or evolved network) after UE attaches to the network. Then, the UE registers with another access network when the UE moves to the another access network. As such, the UE may register with both access systems. After that, when the UE moves between corresponding RA or TA of these two networks, the UE may not initiate any registration procedure. Both the access entities in these two access systems with which the UE registers contain UE context.
Now, the procedure of UE first attaching to the SAE and then moving to 2G/3G is illustrated below.
As illustrated in FIG. 3, at step 301, the UE attaches to SAE, sending an “attach request” message to MME.
At step 302, the MME may acquire context from HSS and initiate an authentication procedure with the UE.
At step 303, the UE returns an authentication response to the MME. If the authentication passes, it indicates that the UE has registered with MME successfully. The MME assigns an SAE temporary mobile subscriber identity (S-TMSI)/SAE routing area (S-RA, i.e., TA) and a default IP to the UE. The S-TMSI denotes a temporary mobile subscriber identity of the SAE. S-RA demotes the RA of the SAE, i.e., TA.
At steps 304 and 304′, the MME may register with HSS (if MME already contains the UE context, there is no need for the MME to acquire the context from HSS).
At step 305, the MME confirms that the UE has attached to the network successfully and allows the UE to enter. The MME assigns S-TMSI/S-RA to the UE and sends information of the default IP to the UE.
At step 306, after the UE switches from RAT to 2G/3G, the UE initiates an RAU procedure and carries S-TMSI/S-RA assigned by the MME to the SGSN (and may also carry parameters such as TMSI/RA assigned by the SGSN).
At steps 307 and 307′, the SGSN may send an SGSN Context Request message to associated MME to request UE context. After the MME receives the request message, the MME sends the associated context to the SGSN. Such procedure is referred to as a Context Retrieval procedure.
At step 308, authentication procedure may be performed. The SGSN may register with HSS, as illustrated in steps 309 and 309′ (SGSN may not register with HSS, but may treat MME as HSS).
At step 310, the SGSN confirms the receipt of the context and may trigger the MME to transfer data.
At step 311 and 311′ the SGSN may update Packet Data Protocol (PDP) context with MME because MME, at the user plane, is similar to an original GPRS Gateway Support Node (GGSN).
At step 312, the SGSN assigns U-TMSI (UMTS TMSI, Temporary Mobile Subscriber Identity of UMTS)/U-RA (Routing Area of UMTS) and S-TMSI/S-RA to the UE. After that, no update registration message needs to be sent when the UE moves between U-RA and S-RA. The U-TMSI denotes a temporary mobile subscriber identity of the 2G/3G. U-RA demotes the RA of the 2G/3G.
At step 313, the UE returns an RAU completion message.
The procedure that the UE first attaches to 2G/3G and then moves to SAE is similar to the procedure that the UE first attaches to SAE and then moves to 2G/3G as illustrated in FIG. 4, which will not be detailed herein.
Briefly, the UE first attaches to the SGSN. The SGSN registers with HSS. Then, the UE enters SAE and initiates RAU and retrieves context from SGSN. The MME registers with HSS and assigns S-RA/S-TMSI to UE. The UE does not need to initiate a location update/registration message when moving between the registered RA and S-RA (in terms of TA, RA, UE may be assigned with a plurality of areas of SAE or 2G/3G, such as several S-RAs. Then, the UE does not need to initiate the update message when moving between the registered areas assigned by the network). When the UE moves to areas beyond registered S-RA/RA, the UE needs to initiate an update message. It should be noted that if SGSN is not replaced, the SGSN registration procedure may be unnecessary.
It is discovered that the above schema encounters at least the following issues in practical application. The network side may page UE in an unnecessary paging area, reducing efficiency for paging UE.
The root cause behind such problem is that in the current registration procedure, after the UE enters an RAT network, the UE performs registration and is assigned with TA/RA of the RAT network. After the UE enters another RAT network, the UE initiates an update procedure and is assigned with RA/TA of another RAT network. Then, the UE does not need to initiate the update procedure when moving between the registered RA and TA. When the UE enters a new RA or TA, the UE needs to initiate an update message. The SGSN/MME of the new RA/TA establishes an association with an access entity (MME/SGSN) of another RAT network. Accordingly, the UE does not need to initiate an update message when moving between the new RA/TA and the TA/RA assigned by the access entity of another RAT network.
As illustrated in FIG. 5, the TA is a registered area of SAE while RA is a registered area of UMTS. According to the current schema, the UE registers with MME when entering TA1 and initiates an UMTS location update after entering RA1 and registers with SGSN. Then, the UE does not need to initiate a location update procedure when moving between TA1 and RA1. As such, location update procedures due to ping-pang movement between two RAT networks can be saved. That is, the notion of TA may help to avoid ping-pang update due to different TAs in one RAT.
After UE moves to RA2, the UE initiates a location update. Then, the UE does not need to initiate a location update procedure between TA1 and RA2 (when UE moves back to RA1, the UE still needs to initiate a location update. After that, the UE does not need to initiate a location update when moving between TA1 and RA1).
If UE does not need to initiate a location update procedure when moving between TA1 and RA2, and the UE will initiate a location update procedure again when moving back from TA1 to TA2. After that, the UE does not need to initiate a location update procedure when moving between TA2 and RA2.
Likewise, when UE moves to TA3, TA4 till TA5 again, the UE does not need to initiate a location update procedure when finally moving between TA5 and RA2.
However, it can be seen from the figure that it is impossible for the UE to move directly between TA5 and RA2. In addition, the MME managing TA5 may not be associated with the SGSN managing RA2 (e.g., the MME and the SGSN belong to different Public Land Mobile Networks, and have no roaming interface, or due to distance reason, the “associable SGSN list” configured on the MME does not include SGSN which RA2 belongs to). Therefore, a signaling procedure between TA5 and RA2 is not necessary. Since the UE can only enter an area around TA5 in a next step and the UE is unlikely to enter RA2, it is meaningless to associate the SGSN of RA2 with the MME of TA5. However, RA2 still needs to be paged during paging period, which may cause a mass of paging and reduce efficiency for paging UE.
Alternatively, in practice, UMTS is an all-covered network. SAE is a network covering spots of interests, as illustrated in FIG. 6. After UE registers with TA1 and RA1, the UE moves from RA1 to RA2 and to RA3. The UE does not need to initiate an update procedure when moving between TA1 and RA3. Alternatively, after UE registers with TA1 and RA1, the UE moves from TA1 to TA2 and to TA3 and to TA4. Then, the UE does not need to initiate an update procedure when moving between RA1 and TA4.
Usually, the area with which the UE registers (after registering with two RAT networks) is referred to as UE registered area or non-update area. With no optimization such as priority residence, the paging area of UE is the UE registered area (non-update area). However, actually, since UE may not move directly between these two RA/TA (location update procedure is bound to be incurred during moving), the necessary paging area of UE is just the registered area of RAT network where the UE currently locates. Therefore, the network side may page UE in an unnecessary paging area, reducing efficiency for paging UE.
After ISR is activated, the HSS may record entity information of two systems. That is, the HSS may record information of SGSN and MME with which the UE registers, i.e., dual registration. However, single registration refers to that the HSS may only record information of the entity in one system after ISR is activated (i.e., record the information of the entity with which UE initiates the update most recently). However, information of entities in other system with which the UE registers is stored in another system entity. If the UE first registers with 2G/3G first, then the HSS records information of SGSN with which the UE registers (a location update message is sent to HSS via SGSN). When UE moves to another RAT SAE system and initiates a location update, the UE again registers with MME in the SAE system. The ISR is then activated. Also, the MME sends a location update to HSS. The HSS records the information of MME and deletes the information of SGSN. However, the information of SGSN is stored in the MME. The SGSN and MME all record UE information. However, HSS only saves entity information of one system.